initial_state_ramp_up.h

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//
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// Copyright (C) 2022 - 2026 by the ryujin authors
//
 
#pragma once
 
#include <ryujin/base/compile_time_options.h>
#include <ryujin/typed/initial_state.h>
 
namespace ryujin
{
  namespace EulerInitialStates
  {
    template <typename Description, int dim, typename Number>
    class RampUp : public InitialState<Description, dim, Number>
    {
    public:
      using HyperbolicSystem = typename Description::HyperbolicSystem;
      using View = typename HyperbolicSystem::template View<dim, Number>;
      using state_type = typename View::state_type;
      using state_type_1d =
          typename HyperbolicSystem::template View<1, Number>::state_type;
 
      RampUp(const HyperbolicSystem &hyperbolic_system,
             const std::string subsection)
          : InitialState<Description, dim, Number>("ramp up", subsection)
          , hyperbolic_system_(hyperbolic_system)
      {
        t_initial_ = 0.;
        this->add_parameter("time initial",
                            t_initial_,
                            "Time until which initial state is prescribed");
 
        t_final_ = 1.;
        this->add_parameter("time final",
                            t_final_,
                            "Time from which on the final state is attained)");
 
        primitive_initial_[0] = 1.4;
        primitive_initial_[1] = 0.0;
        if constexpr (View::have_energy_equation)
          primitive_initial_[2] = 1.;
        this->add_parameter("primitive state initial",
                            primitive_initial_,
                            "Initial 1d primitive state [rho, u, p] (or [rho, "
                            "u] for the barotropic Euler module)");
 
        primitive_final_[0] = 1.4;
        primitive_final_[1] = 3.0;
        if constexpr (View::have_energy_equation)
          primitive_final_[2] = 1.;
        this->add_parameter("primitive state final",
                            primitive_final_,
                            "Final 1d primitive state [rho, u, p] (or [rho, u] "
                            "for the barotropic Euler module)");
 
        const auto convert_states = [&]() {
          const auto view = hyperbolic_system_.template view<dim, Number>();
          state_initial_ = view.from_initial_state(primitive_initial_);
          state_final_ = view.from_initial_state(primitive_final_);
        };
        this->parse_parameters_call_back.connect(convert_states);
        convert_states();
      }
 
      auto compute(const dealii::Point<dim> & /*point*/, Number t)
          -> state_type final
      {
        state_type result;
 
        if (t <= t_initial_) {
          result = state_initial_;
        } else if (t >= t_final_) {
          result = state_final_;
        } else {
          const Number factor =
              std::cos(0.5 * M_PI * (t - t_initial_) / (t_final_ - t_initial_));
 
          const Number alpha = factor * factor;
          const Number beta = Number(1.) - alpha;
          result = alpha * state_initial_ + beta * state_final_;
        }
 
        return result;
      }
 
    private:
      const HyperbolicSystem &hyperbolic_system_;
 
      Number t_initial_;
      Number t_final_;
 
      state_type_1d primitive_initial_;
      state_type_1d primitive_final_;
 
      state_type state_initial_;
      state_type state_final_;
    };
  } // namespace EulerInitialStates
} // namespace ryujin